Women who give birth at age 35 or older appear more likely than younger women to deliver premature or low birth weight babies. It was estimated that the increase in premature and low birth weight is partly related to delayed childbirth.
The study was carried out at the University of Calgary Medical School, Canada. The researchers based their findings on data gathered from 284,000 births which included about 29,000 women of 35 years and above. The study of births during the 1990s in the province of Alberta showed that the proportion of births to women aged 35 and older grew more than 50% between 1990 and 1996. The researchers calculated that such delayed childbearing accounted for 78% of the increase in low birth weight babies in Alberta during the study period.
This analysis suggests that delayed childbearing is responsible for a substantial proportion of population changes in rates of low birth weight and preterm delivery. The team's findings provide a better understanding of Alberta's rates of low birth weight and preterm delivery, which are among the highest in Canada. They highlighted the increased risks relatively older mothers-to-be might face compared with younger moms. Those aged 35 and older were 20% to 40% more likely to have a baby weighing less than 2,500 grams, or about 5.5 pounds. They were also 20% more likely to give birth before the 37th week of pregnancy.
Babies who are born prematurely or at a low weight are more likely to require neonatal intensive care and may face long-term problems such as developmental delays. Despite their higher relative risks most older women in the study had normal-weight full-term newborns. Fewer than 9% of these women had their babies before week 37, compared with roughly 7% of women younger than 35. This study is not designed to tell women at what age they should have children or to discourage women over the age of 35 from having children. Instead research like this is intended to give women information they need in deciding whether to delay pregnancy. This work encourages us to explore in more detail how we can identify women who may be at risk for low birth weight babies or preterm deliveries.
Pediatrics March 2002, Vol. 101(3)